Authorities say the teen was killed as he stood in the road with his younger brother talking to a school bus driver about getting on the bus.
Charles Cook had missed an earlier bus and was trying to flag down driver Courtney Pinson when a car came down the hill in a drizzling rain shortly before 7:30 a.m.
The car, driven by 21-year-old Juan Teran of Dalton, struck Cook, slamming him into the windshield.
His brother was not injured. Georgia State Patrol SGT Joe Harrison says no charges had been filed against Teran as of Thursday evening.
The school bus driver was placed on administrative leave with pay, standard procedure pending an investigation, according to Richard Schoen, director of student services for Whitfield County Schools.
Neither Schoen nor Harrison would say if Pinson had extended the stop sign from the driver's side of the bus.
Georgia law requires motorists to stop when school buses have the sign extended for loading or unloading.